Clean water is necessary for human health and well being. Evaporating and condensing of water, in natural processes such as the water cycle and in the man-made processes of distillation and desalination, cleans water of most or all impurities. However, the high specific heat of water and other liquids of moderate volatility means an expensive expenditure of energy is required, for distillation and desalination.
Many inventions have used a vacuum to reduce vapor pressure and achieve evaporation with less energy for heating. These include use of a barometric column of condensate, a technique derived from barometers and the ancient observation that water cannot be siphoned at a height exceeding 10.3 meters—“nature abhors a vacuum,” as Aristotle theorized. In these inventions, the barometric column of condensate has been used to pull an initial vacuum, and/or as a pulling counter-weight to slow the loss of vacuum in an evaporative stage, and in other novel manners.
Many inventions have used solar energy and ambient temperature differences, alone or in combination with vacuums, to increase the heat-energy efficiency of evaporation. Related inventions have used various mechanical devices, series of chambers, stop-cocks and valves, gauges and timing sequences to achieve greater efficiency of evaporation and condensation. Some have used vents, for filling the system initially, and for periodic evacuation of air entrained in water, usually using mechanical vacuum pumps. The Newcomen engine used a “snifting clack,” a valve so-named because it sounded like a congested man breathing out his nose, to relieve air entrained in water that built up in his vacuum-driven piston cylinder. Some of the inventions require a high degree of oversight and control in their operation, and most need periodic system purges and maintenance of various pumps and active devices.
There may be a need and a market for a simple system that is self-starting and self-stopping. Preferably, such a system would not require either energy-consuming devices for its operation or need for regular oversight to function. The system would also use the force of gravity working on a column of condensed water to create vacuums and reduce heat energy expenditure. Preferably, the thermal “delta” or difference would create an evaporation region and a condensation region which could be established passively, with low-cost or free energy. A system is needed that incorporates all the aforementioned features and yet still scales well, to be affordable to private citizens as well as public utilities or private corporations. A system, finally, designed to use natural changes in outdoor temperature to its advantage, would be robust, forgiving, and desirable.